The present invention relates to the configuration of a semiconductor chip having a circuit formed thereon. More particularly, the present invention pertains to a semiconductor device constituted by a plurality of semiconductor chips connected together with a high degree of accuracy.
1. Field of the Invention
There have heretofore been semiconductor devices adapted to receive the light reflected from a document irradiated with light and convert the received light into an electric signal. One type of such conventional semiconductor device is arranged such that a plurality of semiconductor chips are connected together to form a continuous or elongated line sensor having the same size as that of a particular document so as to read the document with a magnification of xl. The present invention provides an improvement in this type of semiconductor device wherein the configuration of a cross-section of each of a plurality of semiconductor chips connected together is specified which in cross-section has a ridge intersecting the connected end surfaces of a plurality of semiconductor chips and which is taken along the direction in which the semiconductor chips are arranged. More specifically, the above-described cross-section has the shape of a trapezoid having a long side defined by the side of the cross-section which is in turn defined by the obverse surface of the chip on which the circuit is formed, and a short side defined by the side of the cross-section which is in turn defined by the reverse surface of the chip. By virtue of this arrangement, a plurality of semiconductor chips can be connected together with a high degree of accuracy. In addition, if the present invention is applied to a semiconductor chip having a light-emitting element, it is also possible to realize a high-density light source for a contact-type LED printer.
2. Description of the Prior Art
Recently, various kinds of contact-type image sensors used as small-sized image input devices for business machines, computers, etc. have actively been developed. Contact-type image sensors need to be a continuous or elongated line sensor which has the same size as that of a particular document for the purpose of reading the document at a magnification of xl. To this end, there is a trend to make efforts to realize an elongated contact-type image sensor by connecting a plurality of silicon IC chips for which the process technique has already been established and which are excellent in reliability.
In this case, the error in connection between each pair of adjacent IC chips limits the resolving power of the contact-type image sensor when reading. To realize a high-resolving power contact-type image sensor, the condition of the end surfaces (diced surfaces) of each IC chip is a very important factor. In addition, since the higher the resolving power, the smaller the distance between each pair of adjacent sensors, it is necessary to precisely maintain the distance between the sensors respectively located on both sides of each joint.
A typical conventional method of cutting an IC chip will be explained below with reference to the accompanying drawings.
FIG. 2 shows a conventional cutting method. As shown in FIG. 2(A), a semiconductor substrate 1 is cut on the obverse side using a dicing saw in such a manner that the reverse side of the substrate 1 is left uncut with a thickness of several tens to several hundreds of microns. Then, a pressure is applied to the substrate 1 to break the same so as to be divided into chips. With this method, however, the end surface of an uncut portion cannot be made uniform due to, for example, the crystalline properties of the substrate and the way in which the pressure is applied to the substrate. This is shown by the non-uniform crack lines in FIG. 2(b). FIG. 2(C) shows a plurality of chips cut by the conventional method and connected together. The reference symbols t.sub.1, t.sub.2 and t.sub.3 shown in FIG. 2(C) respectively represent chip connection errors. As illustrated, the chip spacings are not uniform, and there are large variations in the chip spacing. As a result, the sensor spacing between each pair of opposing connection surfaces becomes non-uniform, which means that it is impossible to obtain a contact-type image sensor of high resolving power and high accuracy.
There is another prior art method known as the through-cut method which has improved the above described conventional method. According to the through-cut method, a semiconductor substrate is cut to the reverse surface at a stretch in a dicing step without any portion of the substrate left uncut. This through-cut method will be explained below with reference to FIG. 2(D). The reference numeral 1 denotes a semiconductor substrate having circuits formed thereon, and the numeral 2 denotes an adhesive sheet. The adhesive sheet 2 is provided for the purpose of effecting full-cutting and of protecting the support stage of a dicing saw from being damaged. This method, however, still fails to completely eliminate uncut portions. FIG. 2(E) shows a cut surface of a semiconductor chip cut by the through-cut method. As a result of observation using a scanning electron microscope, it has been found that there are several chippings 10 of 5 .mu.m in the shape of projections near the reverse surface and that few dust particles 11 regarded as silicon powder particles are attached to the side surface. FIG. 2(F) shows a plurality of such IC chips connected together. The chip connection errors t.sub.1, t.sub.2 and t.sub.3 are reduced and uniformity is improved as compared with the conventional method shown in FIG. 2(C). However, the distance between each pair of adjacent chips is not satisfactorily small. In order to overcome these problems, still another dicing method has already been proposed. This prior art will be explained below with reference to FIGS. 2(G) and 2(H). In a first step, through-cutting is effected from the obverse surface of a semiconductor substrate 1 as shown in FIG. 2(G). After the completion of this step, the obverse surface is washed, dried, and an adhesive sheet 2 is stuck to the obverse surface, while the adhesive sheet 2 attached to the reverse surface is separated. In a second step, the substrate 1 is diced from the reverse surface using a blade 4 having a width somewhat wider than the blade 3, employed in the first step. This step is shown in FIG. 2(H). FIG. 2(I) shows a plurality of IC chips thus obtained and connected together. Thus, the uniformity of the gaps at the joints is improved, and the distance between each pair of adjacent IC chips is also reduced by a large margin, so that the degree of accuracy in connection is increased. This dicing method is, however, complicated as compared with the other conventional methods, and it is therefore difficult to improve the yield in the dicing step. In addition, it is impossible to eliminate the presence of dust particles 11 attached to the cut surfaces.
The above conventional method is disclosed in the following patent:
Japanese application Patent No. 12346/1984 applied Jan. 25, l984.